The present invention relates to an X-ray apparatus using X-ray diffraction, X-ray fluorescence, or X-ray transmission to identify or chemically analyze a microscopic area of a sample non-destructively and to scan the sample surface for performing area or line analysis of the sample.
The Japanese Patent Provisional Publication No. SH059-72052 discloses one example of conventional X-ray analyzing apparatus. In this apparatus, a hollow capillary whose inside cross section has the form of a circle, an ellipse or a polygon and whose inner surface is parallel and mirror-finished is extended from an X-ray source to a sample fixed at the center of a sample stage composed of a three-axis precise movement mechanism and a biaxial rotational mechanism which are combined. An X-ray diffraction image and fluorescent X-rays of a microscopic area of the sample are received by a film or a position sensitive proportional counter or a guide tube for measuring X-ray fluorescence. According to this structure, when a tiny and thin sample is to be analyzed, the hollow capillary extending from the X-ray source is brought close to the sample, and a thin X-ray beam approximately as thin as an internal diameter of the hollow capillary is irradiated on the sample. The fluorescent X-ray emitted from the sample is received by the guide tube for measuring fluorescent X-rays and measured by a semiconductor detector arranged at the end of the guide tube. On the other hand, the diffraction X-rays are measured by the film or the position sensitive proportional counter. By the above, materials in the microscopic area are identified and chemically analyzed, and the sample is area-analyzed or line-analyzed by a linear movement mechanism.
Another prior art apparatus is, for example, disclosed in the Japanese Patent Provisional Publication No. SH061-22240. This prior art apparatus is composed of: a collimator for delivering a thin X-ray beam onto a minute part of a sample; a detachable spectrocrystal which is provided so that fluorescent X-rays emitted from a sample surface may be incident on the spectrocrystal; and an incident position sensitive X-ray detector in an arc provided so as to move around either a point which is symmetric to the microscopic area with respect to the surface of the spectrocrystal or the microscopic area. In this structure, when a tip of the collimator is brought in close proximity to the sample, a thin X-ray beam is formed and the beam irradiates the microscopic area of the sample. The microscopic area emits fluorescent X-rays, which are reflected by the spectrocrystal and whose energy is measured from a difference in incident position by the position sensitive X-ray detector in an arc which was moved around the point symmetric to an X-ray irradiation area with respect to the spectrocrystal. On the other hand, diffraction X-rays are measured by the incident position sensitive X-ray detector in an arc which was moved around the X-ray irradiation area. Thereby, materials in the microscopic area are identified and chemically analyzed. The material is moved by a rectilinear, or straight line, movement mechanism to be area-analyzed or line-analyzed.
In a manipulator for manipulating a thin X-ray beam, the intensity of the beam is greatly attenuated, depending on the energy and optical distance thereof, even when the beam energy is 5 keV or more. Therefore, to fabricate an X-ray optical system by using a visible light optical alignment bench for an X-ray optical element is difficult, so that a manipulator for exclusive use with X-ray optical systems to control the attenuation of X-rays in the air to a minimum using vacuum technology has been used.
An exemplary X-ray mirror manipulator is constructed as shown in FIG. 5. That is, it comprises a mirror mount tube 43 formed integral with the X-ray mirror, six vacuum-sealed micrometers 40 (four of which are visible in FIG. 5), a vacuum tube 46 for fixing the micrometers in a vacuum, a vacuum bellows 45 for securing rectilinear movement of mirror mount tube 43 in the longitudinal direction, a linear stage mechanism 41, vacuum flanges and supports 39, and an X-ray window 42 for separating the interior of tube 46, which is under a vacuum, from the surrounding atmosphere. The manipulator for an X-ray optical element performs bidirectional gates and bidirectional rectilinear movements on the inserted mirror mount tube 43 with respect to the vacuum tubes by means of the six micrometers, and linearly moves the vacuum tube 46 with respect to the flanges and supports by using the rectilinear stage mechanism 41. Accordingly, it is shown in FIG. 5 that the X-ray mirror in the mirror mount tube 43 in a vacuum-sealed state can be aligned in pentaaxial directions by the operation through the X-ray window in the atmosphere.
Further, X-ray position detectors are of two types depending on the way in which they detect fluorescent X-rays, transmission X-rays or X-ray diffraction intensity: a pulse counting type in which X-ray light quanta are counted one by one and an integral counting type in which the intensity of X-rays received by the detector for a predetermined time period is integrated for counting. Typical examples of position sensitive detectors having a position detection function capable of recording one-dimensionally or two-dimensionally location distribution of the X-ray density are a one-dimensional and a two-dimensional proportional counter tube, an X-ray film, an imaging plate, an X-ray television, a CCD X-ray sensor. Above all, the proportional counter tube, which is a pulse counter type detector, has excellent features to have one-dimensional or two-dimensional position resolving power and energy resolving power. On the other hand, the integral counting type detector is excellent in position resolving power for position detection, and an X-ray film is one of the examples which is most frequently used.
However, the Japanese Patent Provisional Publication No. SHO59-72052 discloses an apparatus in which a hollow capillary leads X-rays from an X-ray source to the center of a sample stage. Since this hollow capillary is a non-imaging optical element, it has a very large aberration. Further, when a distance of a few mm or more is kept between a sample and the hollow capillary, it is impossible to form X-rays into a thin X-ray beam having a diameter of .mu.m order. In order to form a thin X-ray beam of .mu.m order in accordance with the above structure, it is necessary that an inner diameter of the capillary which is equivalent to an X-ray outgoing pupil should be not more than the diameter of the area to be measured and also that a tip of the capillary should be arranged in close vicinity to the sample stage. However, if the tip of the capillary is in the vicinity of the sample stage, not only is the size of the sample restricted but also the permissible rotational angle of the sample stage is restricted. If the thickness of the hollow capillary is made smaller in order to avoid the restriction on the rotational angle, the hollow capillary transmits the X-rays and the effective diameter of the X-ray beam becomes larger than a required value, which results in a problem that a microscopic area cannot be analyzed.
Moreover, in the above prior art, a three-axis precise rectilinear movement mechanism is incorporated in a rotational mechanism, so that the size of the sample stage becomes smaller and the movement distance of the three-axis precise rectilinear movement mechanism is as short as a few millimeters or less.
Further, an apparatus disclosed in the Japanese Patent Provisional Publication No. SHO61-22240 uses a collimator for applying a thin X-ray beam from an X-ray source to a sample surface. A microscopic area of the sample irradiated with the X-rays depends on an inner diameter of the collimator and a distance between the collimator and the sample surface. Therefore, in the same way as the former publication, obtaining a minimum diameter of the X-ray beam requires a small inner diameter and also requires the collimator and the sample surface be in close proximity. Therefore, also in this case, the rotational angle of the sample surface is restricted by the collimator itself, thereby prohibiting a large rotational angle for the sample surface. Moreover, since the embodiment of this publication has only one rotational axis for the sample, it is difficult to measure diffraction X-rays when the number of crystal grains is small in the microscopic area irradiated with the X-rays.
As to the above two publications, samples to be measured are restricted to small ones. The reason is, as above mentioned, that the sample scanning distance of the sample stage is short and that sample gate rotation is restricted by the collimator or the hollow capillary. Because these X-ray optical elements perform bidirectional rectilinear movements and bidirectional gates with 6 micrometers, it wastes movement parameters. Next, since it performs the gate of the X-ray mirror only by the rectilinear mechanism of the micrometers, it is extremely difficult to operate the rectilinear components and the gate components independently of each other with respect to the pentaaxial alignment components of the X-ray mirror, and it is thereby difficult to perform alignment of the X-ray mirror. Further, since in FIG. 5 the rectilinear and gate operations of the mirror mount tube are performed inside the vacuum tube, it is necessary for each micrometer 40 to have a long stroke 44 and for the vacuum tube 46 to be given large dimensions. Further, the flanges and supports must necessarily be large, so that the manufacturing cost increases and the manipulator itself becomes large and heavy, no matter how small the X-ray optical element is. Also in the case of designing an optimal optical system, even when it is necessary to employ an X-ray mirror with a short operating distance and to insert a spatial filter midway in the optical distance determined by the X-ray mirror, there are still cases where these requirements are limited by the size of the manipulator. Concerning the structural problem, in addition to a problem as to the size of the system, the mounting and dismounting of the manipulator are not easy. Therefore, it is difficult to measure a thin film on a silicon wafer a few cm square or more, and a sample should be a minute chip.
Further, in an X-ray position detector, the method for detecting X-ray diffraction patterns depends on the wavelength of X-rays to be used and the kind of the X-rays, for example, characteristic X-ray and white X-rays. Generally, a one dimensional or two dimensional proportional counter tube which is a pulse counting detector has the limitation that counting loss due to dead time happens at a high counting rate and moreover proportion resolving power is not sufficient.
On the other hand, X-ray films and X-ray televisions which are integral counting detectors have low sensitivity, a narrow dynamic range and poor linearity. These shortcomings are less in an imaging plate, but after an X-ray image is recorded on the imaging plate, a He-Ne laser is used and a focused laser beam two-dimensionally scans on the imaging plate to read an X-ray latent image of the above X-ray image. The fluorescent intensity of the image is measured by a photomultiplier tube, and its output is multiplied by a logarithmic amplifier. Further, the output is converted into numeric values by an A/D converter, and then the image is recomposed by a computer. Apparatus of this type tends to cause readings to take much time and the size of apparatus is required to be large.